PURPOSE: To provide a direct-current converter which can reduce a useless power.

CONSTITUTION: This direct-current converter for converting an input direct- current power into a direct-current power required for a load is provided with a main converter means 5 for converting an input direct-current power into a direct-current power required for a load, an auxiliary converter means 6 for converting an input direct-current power into a direct-current power required within the direct-current converter 5, an auxiliary control means 11 for giving the instruction of operation or non-operation to the auxiliary converter means 6 and a main control means 8 for giving the instruction of operation or non- operation to the main converter means 5 in accordance with the output of the auxiliary converter means 6 at the time of operation or non-operation by the auxiliary control means 11.